This invention relates to plastic containers or similar receptacles and particularly those in which such containers are made of orientable, multilayered thermoplastic materials forms by solid state pressure forming processes. Containers of this character made in accordance with the subject invention are composed of a cylindrical sidewall with a bottom endwall integral therewith and an opening with a flanged peripheral portion surrounding the opening thereof, the flanged portion being especially contoured to receive a metal or thermoplastic closure.
Solid state pressure forming is a special process used to form oriented plastic containers, especially multilayered thermoplastic containers. In general, a container is produced by forming a circular preform which in turn is forged from a blank plastic chip, the preform thereafter being thermoformed into the finished container. During the forging operation, the rim of the container is held by a gripping fixture that acts to clamp the preform while the center portion of the preform is maintained at a predetermined temperature for thermoforming step. It will be appreciated that there will be a high degree of orientation built into the finished container through such forging of the preform and thermoforming process. As a result containers so made have improved strength and stress crack resistance.
Generally, a conventional closure is sealed to a receptacle or container by means of a seaming operation. However, a number of problems may arise in effectively sealing such containers with a closure. For example, when a single seam is used in the absence of special chemical sealants the single seam is not sufficient in that it does not effectively seal to render the container leakproof. When double seaming iis used to seal metal closures to thermoplastic containers, it is generally found that such sealed containers likewise present some leakage problem due to a number of reasons, especially in the tendency of a metal closure to cut through the plastic flange during the sealing operation which eventually results in the release of the contents of the container. Furthermore, during shipment when thermoplastic containers are accidentally dropped they are often deformed to the extent that their products seep or ooze out. Such leakage results in loss of product as well as damage to the appearance of the container and label.
Various attempts have been made to avoid these problems. Admittedly, it has been found relatively difficult to provide satisfactory means by which conventional closures can be successfully attached to containers of the thermoplastic type. Certainly, any means of attachment employed for uniting the container body with the closure must be one which will positively provide a leakproof container. In addition, the closure should be so attached as to somewhat stiffen the entire container body to provide as rigid a structure as possible and be so attached as to avoid disconnection during the normal use of the container.
In the U.S. Pat. No. 2,196,206 to Foss a container is described having a flange with a circumferential line of weakening disposed at the base of the flange and when this flange is double seamed to a closure it forms a fractural seam so that the container remains tamperproof in that the container cannot be opened and resealed to assume an appearance identical to the original container. It will be appreciated that the flange configuration herein disclosed is nonfractural and is reversely bendable. In the prior art, attempts have been made to join a closure with a plastic flange configuration in forming a sealed container, especially a plastic container having low gas permeability. In U.S. Pat. No. 3,923,190 to Roth one approach of interfolding a thermoplastic flange portion with a closure is the use of a preform or billet having its peripheral area devoid of any plastic material of low permeability. The subject invention does not require such a drastic approach. Since the patentee does not use a multilayered structure wherein the layers are parallel to the walls of the container as would be produced by conventional coextrusion techniques but a layered structure wherein the layers are at right angle to the walls the patentee's approach would apparently be impractical in the environment of this invention. As disclosed and claimed herein, a preform formed from a multilayered structure produced by coextruding a plurality of polymeric material, even with a low gas permeable layer, can be readily utilized and interfolded.